1. Field of the Invention
The present invention relates to aromatic polyamides which have high temperature resistance and good mechanical properties, and which are thermoplastically processible.
2. Discussion of the Background
Aromatic polyamides with the repeating unit: EQU --CO--Ar--CO--NH--Ar'--X--Ar"--Y--Ar"--X--Ar'--NH-- (I)
not only display high temperature resistance and good mechanical properties; they are also thermoplastically processable (see Elias/Vohwinkel, New Polymer Materials for Industrial Use, 2nd Ed. Carl Hanser Verlag 1983, pp. 242 ff). In repeating unit (I), X and Y alternatively stand For an ether and a sulfonyl group, and Ar, Ar' and Ar" stand independently of one another for the para- and meta- phenylene group.
Prior art processes for producing aromatic polyamides include the following:
1. Low temperature solution polycondensation by reacting aromatic dicarboxylic acid dichlorides with aromatic diamines in polar solvents (See U.S. Pat. Nos. 3,287,324; 3,541,056; 3,600,350; 3,819,587; 3,767,756; 3,869,429; 3,673,143; 3,817,941; 3,063,966; and German No. AS5 22 19 703).
The subject of U.S. Pat. No. 3,859,252 is thermoplastic condensation polymers with an aromatic bisamide structure. The compound in which R=H, X=SO.sub.2 and Y=O contains repeating unit (I). It is produced from isophthaloylchloride and the corresponding diamine.
2. Interface polycondensation by reaction between an aromatic dicarboxylic acid dichloride and an aromatic diamine at the interface of an organic and an aqueous phase (See German No. OS 19 08 297 and OS 23 25 139; and German Pat. No. 30 06 899).
Aromatic polyamides can also be prepared by the reaction of aromatic dicarboxylic acids with aromatic diisocyanates (German Pat. No. 19 28 435) and by reacting aromatic dicarboxylic acid diaryl esters with aromatic diamines.
For example, Brode et al. describe the preparation of 4,4'- [sulfonylbis (p-phenyleneoxy)] to dianiline (X=0, Y=SO.sub.2) from p-aminophenol and 4,4'-dichlorodiphenylsulfone and its condensation with aromatic acid chlorides such as terephthalic acid chloride, for example, to produce aromatic polyamides with glass temperatures (Tg) between 230.degree. and 320.degree. C. (See Polymer Prepr. Am. Chem. Soc. Div. Pol. Chem. 15, 761 (1974) and Adv. Chem. Ser. 142 (1975); See CA 84, 5530 s).
This process has the disadvantage that it calls for the use of activated, hard-to-handle monomers, such as dicarboxylic acid chlorides.
Processes are also known by which one can obtain aromatic polyamides directly by reaction of aromatic dicarboxylic acids and aromatic diamines in the presence of aromatic phosphites. N-methyl acid amides, particularly N-methylpyrrolidone, have been found to be good solvents for this process. With other dipolar aprotic solvents, such as dimethylsulfoxide, no polymer amides are obtained (See F. Higashi et al., J. Polym. Sci., Polym. Chem. Ed. 18, 1711 ff (1980).
In a summary (See S. M. Aharoni et al., J. Polym. Sci., Polym. Chem. Ed. 22, 2579 (1984), it is concluded that:
(i) the phosphite to be used must contain aryl groups and should preferably be a triphenyl phosphite;
(ii) the aryl phosphites must be used in at least such quantities that for each mole of amide to be substituted, one mole of a compound containing the grouping EQU Ar--O--P&lt;
is added, since this grouping will be consumed during the course of the reaction, and this reaction is the driving force behind the transformation; and
(iii) pyridine is not required for the reaction, but does have the effect of speeding up the reaction.
Finally, in European Pat. No. 0 099 997, a process for producing aromatic polyamides is disclosed in which aromatic dicarboxylic acids are reacted with aromatic diamines in a polar solvent in the presence of a dehydrating catalyst, such as a phosphorus-containing compound, for example. The polyamides disclosed cannot be thermoplastically processed because of their high softening points, which lie in the area of the decomposition temperature or even higher. If electron-rich aromatic diamines, such as 4,4'-diaminodiphenylether, are used in this process, long reaction times are required to obtain products of high molecular weight, and these products are heavily colored due to the formation of unidentified by-products. If, on the other hand electron-poor diamines such as 4,4'diaminodiphenylsulfone are used, the process according to European Pat. No. 0 099 997 fails to work altogether. All that is obtained are heavily colored oligomers.
In addition to these processes, in which condensation is performed in a solvent, attempts have also been made to produce polyamides in the melt. Thus, U.S. Pat. No. 3,109,836 discloses a process for producing polyamides with repeating units of (CO--Ar--NH) that consists of heating acetamidobenzoic acid for three hours in a vacuum at 200.degree. to 300.degree. C.
Contrary to the allegations in this patent, this process does not yield thermoplastically processable products, since the melting points of the products of the reaction lie in the area of the decomposition temperature or higher.
It has also been suggested that aromatic polyamides can be produced by amidation of acylated aromatic amines in the melt. Apart from the fact that such a proceeding would require the prior production of the acylated amines, the results obtained with this process must be considered highly unsatisfactory. In order to improve processibility, the starting compounds are not purely aromatic compounds, but rather a mixture including aliphatic compounds. The diamines are only partially, not completely acylated. Finally, acetic acid, an acetic anhydride, dimethyl acetamide or another agent is added to the reaction melt to improve the flowability. (See Keske et al., Polymer Prepr. 25, Part XXV, p. 25 (1984) and U.S. Pat. No. 3,654,227).
Even though Buhler's standard work on the subject, Spezialplaste (Specialized Plastics), Akademieverlag, Berlin (1978), states on page 412 that the method of melt polycondensation is not applicable to the preparation of aromatic polyamides from aromatic dicarboxylic acids and simple aromatic diamines, there exists a need for a process for producing aromatic polyamides by just this melt polycondensation method.